There are various embodiments of cleaning heads in the prior art. However, attention was previously seldom paid to the design of frictionless drainage devices for such cleaning heads. WO 2008/151814 describes a drainage device in which the dirt particles and the waste water are carried from the cleaning head into a collection container (“disposal device”) installed rigidly transversely above the material web to be cleaned. The collection container has a slit which extends transversely over the entire width of the material web and through which the cleaning head movable transversely to the material web protrudes via its end into the collection container.
A drawback of the prior art is that the dirt particles and the waste water are deposited on the walls on their way through the drainage device. As soon as too many residues are deposited on the wall surfaces in the drainage device, these must be manually cleaned so that the drainage device does not become blocked.